The present invention relates to pulmonary function testing and, more particularly, to pulmonary function testing by a remote pulmonary function tester which communicates with a central pulmonary function analysis computer.
Pulmonary function testing (PFT) is a general term applied to a group of tests which evaluate the ability of the lungs to perform their normal functions. The most frequently used PFT is spirometry, which is the technique of measuring and recording lung volumes dynamically. Other, more complicated PFT's are usually necessary only when spirometry results are abnormal. These include body plethysmography, helium dilution, nitrogen washout, diffusing capacity, exercise testing, and blood gas analysis.
The spirometric evaluation of lung function is indicated for a number of reasons, such as: determining the presence of lung disease or abnormality of function; determining the extent of abnormality; determining the extent of disability due to abnormal lung function; determining the progression of the disease; determining the category of disease or lesion causing the abnormality; and determining a course of therapy for treatment of a previously diagnosed lung disease.
Spirometry measures two different lung functions: vital capacity and airflow rates. The vital capacity is the volume of air that can be exhaled after a maximum inhalation, measured in liters. The maneuver can be done slowly (SVC, slow vital capacity) or it can be forced (FVC, forced vital capacity). It is important because a number of diseases can result in reductions of the vital capacity. Airflow rates are measured in liters per second (L/s), during forced, or maximal expiration. Expired flows increase rapidly to a peak and then decrease with decreasing lung volume. The traditional graph, as obtained by a water spirometer, plots total volume expired vs. time. The average flow during the first second of expiration is called the FEV.sub.1. It is very reproducible and has become the most frequently used flow rate measurement. FEV.sub.25-75% (formerly called MMEF) is measured to give additional information about flow rates occurring later in expiration. It represents a flow rate slope between forced expiration volume at 25% and at 75% time. This flow rate measures the average flow during the middle half of the forced vital capacity maneuver and is a more sensitive indicator of mild dysfunction but is less reproducible than the FEV.sub.1.
The FEV.sub.1 and FEF.sub.25-75% measure average flow rates. The last decade has shown increasing use of a more precise measurement of instantaneous flow rates. These are graphed by a flow volume curve, which plots flow rate (L/s) against volume (L) up to the total volume exhaled. Instantaneous flow rates at any griven lung volume are readily noted on this curve, and several of these are used to compare a subject's curve, with a "normal" curve: FEF.sub.max , FEF.sub.25%, (Forced Expiratory Flow at 25% of total volume) FEF.sub.50%, and FEF.sub.75%. The shape of the flow volume curve is also important in different diseases but techniques have not yet been developed to meaningfully quantitate the shape of the curves. Thus, there is needed a pulmonary function tester which provides a flow volume curve for interpretation by a chest physician.
The chest physician also compares the numerical values of the above parameters obtained for a subject's lung volumes and flow rates with normal values to determined normalcy or estimate the extent of dysfunction. Predicted normal values are obtained by studies of large populations of "normal" individuals. Normal values are best predicted by the subjects' sex, age, height, and, in the case of children, weight. The above-described parameters are conventionally calculated from the volume-time curves produced by a traditional spirometer. This technique has been recently improved by the development of pneumotac sensors, which directly measure flow rates in L/s and generate flow-volume curves. Electronic integrators are used to obtain volumes, and X-Y recorders or oscilloscopes provide graphic flow-volume curves. These systems, however, are not practical for the primary care physician due to their expense.
Another recent improvement in the field of spirometry has been the development of computerized pulmonary function testers to lessen the burden of physician interpretation of raw test data. Jones et al. in U.S. Pat. No. 3,977,394 describe a computerized unit in which a signal proportional to volume is input from a mechanical spirometer, filtered to eliminate mechanical noise, digitized at 18 samples/sec for computer processing, and used to generate, via computer, a volume time curve, FVC, FEV5 (0.5 sec. after beginning of test), FEF 25-75%, and other test results. Greenwood et al., in U.S. Pat. No. 4,034,743, describe a pulmonary analyzer utilizing a piston-type spirometer and a differentiating circuit to obtain flow rate. A micro-computer is used to calculate the tidal volume and test gases breathed and to calculate FEF with a flow rate detector and volume A-D converter. These devices, however, are rather complicated and expensive and, again, beyond the means of the average physician.
It has been attempted to overcome this problem through the use of remote units connected to a central computer, as disclosed by Vail et al. U.S. Pat. No. 3,896,792 and Griffis et al. U.S. Pat. No. 3,726,270. These units, however, lack the advantages of computer preprocessing, storage, and digitization prior to data transmission. These units also utilize slow analog data transmission, which is expensive in terms of telephone costs.
Aside from the aforesaid difficulties of physician interpretation, pulmonary function testing has suffered difficulties in technician operation of the equipment and patient, or test subject, performance of the required maneuvers. Previous equipment has been difficult to maintain, calibrate, and operate. Subjects often do not give full maximum effort, or may hesitate during test maneuvers.
It is therefore an object of the present invention to provide a remote pulmonary function tester with improved patient and operator feedback.
It is further an object of the present invention to provide a remote pulmonary function tester with microcomputer-controlled data processing for transmission of data to a central computer.
It is also an object of the present invention to provide a remote pulmonary function tester which provides rapid data transmission to and from the remote unit.